Part 1 of 2
Glass, Plastics & Composite Materials
Last reviewed 16 Sept 2026 · 10 min read
Glass
Glass is an amorphous (non-crystalline), transparent or translucent solid made by melting silica with fluxes and stabilisers and cooling it without crystallisation.
Composition (typical soda-lime glass)
| Constituent | Approx. % | Role |
|---|---|---|
| Silica (SiO₂) — sand | About 70–73 | Glass former |
| Soda (Na₂O) — from soda ash | About 13–15 | Flux — lowers melting temperature |
| Lime (CaO) — from limestone | About 8–10 | Stabiliser — makes glass insoluble in water, durable |
| Magnesia, alumina | Small | Improve durability and working properties |
| Colouring oxides | Traces | Iron (green), cobalt (blue), chromium (green), manganese (violet/decolourising) |
Manufacture
- Batching — sand, soda ash, limestone, dolomite and cullet (broken glass, which lowers energy use).
- Melting in furnaces at about 1500 °C.
- Forming — the float glass process (developed by Pilkington): molten glass is poured onto a bath of molten tin, spreading into a flat sheet of uniform thickness with fire-polished parallel surfaces; other methods include drawing, rolling, blowing and pressing.
- Annealing — controlled slow cooling in a lehr to relieve internal stresses.
- Cutting, processing and finishing (tempering, laminating, coating).
Properties
Transparent (or translucent), hard and brittle; high compressive strength but low tensile strength; resistant to most chemicals (attacked by hydrofluoric acid and strong alkalis); impermeable and easy to clean; electrical insulator; good weather resistance; poor resistance to impact and thermal shock (except special glasses); no creep at room temperature; can be recycled.
Types of glass by composition
| Type | Composition / features | Uses |
|---|---|---|
| Soda-lime glass | Silica, soda, lime — cheap, easily melted and shaped | Window glass, bottles, general glazing |
| Potash-lime glass (hard glass) | Potash instead of soda — higher melting point | Laboratory apparatus requiring heat resistance, combustion tubes |
| Potash-lead glass (flint glass) | Lead oxide — high refractive index, brilliant | Optical lenses, crystal ware, decorative glass, radiation shielding |
| Borosilicate glass | Boric oxide — very low thermal expansion, resistant to thermal shock (e.g. Pyrex) | Laboratory ware, cookware, fire-resistant glazing, sealed-beam lamps |
| Fused silica / quartz glass | Nearly pure silica | High-temperature and optical applications |
Glass products for buildings
| Product | Features / uses |
|---|---|
| Sheet (drawn) glass | Cheap window glass, may have slight distortion |
| Float glass | Flat, distortion-free, uniform thickness — standard glazing base for other products |
| Wired glass | Steel wire mesh embedded — holds pieces together when broken, some fire resistance — skylights, fire doors, industrial glazing |
| Toughened (tempered) glass | Heated and rapidly cooled — surface in compression; about 4–5 times stronger than annealed glass; breaks into small blunt granules (safety glass); cannot be cut or drilled after toughening — doors, shopfronts, facades, shower screens |
| Heat-strengthened glass | Intermediate strength; breaks into larger pieces — used in laminated units |
| Laminated glass | Two or more glass layers bonded with a PVB (polyvinyl butyral) or similar interlayer — fragments adhere to the interlayer when broken; safety, security, bullet-resistant (multiple layers), sound reduction, UV filtering — skylights, balustrades, overhead glazing, vehicle windscreens |
| Insulated glazing units (double/triple glazing) | Glass panes separated by sealed air or argon-filled spaces — thermal and sound insulation, reduces condensation |
| Low-emissivity (low-E) glass | Thin metal-oxide coating reflects long-wave infrared — keeps heat inside in cold climates or reduces heat gain |
| Reflective and tinted (solar control) glass | Coatings or body tints reduce solar heat gain and glare — facades in hot climates |
| Frosted, obscured and patterned glass | Sand-blasted, acid-etched or rolled patterns — privacy with light transmission — bathrooms, partitions |
| Glass blocks (hollow glass bricks) | Translucent hollow blocks — non-load-bearing walls admitting light |
| Glass wool and fibreglass | Fine glass fibres — thermal and acoustic insulation, reinforcement in GRP |
| Foam glass | Cellular glass — rigid insulation |
| Structural glass | Glass fins, beams and floors (laminated, toughened) |
| Smart (switchable) glass | Electrochromic or PDLC — tint or opacity changes electrically |
| Self-cleaning glass | Photocatalytic titanium dioxide coating breaks down dirt; hydrophilic surface washes clean in rain |
| Fire-resistant glazing | Specially laminated or ceramic glasses maintaining integrity/insulation for specified periods |
Plastics
Plastics are synthetic (or semi-synthetic) organic polymers that can be moulded into shapes, often with additives such as plasticisers, stabilisers, fillers, pigments and flame retardants.
Thermoplastics and thermosets
| Thermoplastics | Thermosetting plastics (thermosets) |
|---|---|
| Soften on heating and harden on cooling repeatedly — can be remoulded and recycled | Set permanently on heating/curing (cross-linked); cannot be softened again |
| Linear or branched polymer chains | Three-dimensional cross-linked networks |
| Generally tougher, more flexible, lower heat resistance | Harder, more rigid, heat and chemical resistant, brittle |
| Examples: PVC, polyethylene (LDPE, HDPE), polypropylene, polystyrene (including expanded polystyrene), acrylic (PMMA, perspex), polycarbonate, nylon, ABS | Examples: phenol formaldehyde (Bakelite), urea formaldehyde, melamine formaldehyde, epoxy, polyester, polyurethane (rigid foams), silicone resins |
Elastomers (natural and synthetic rubbers — neoprene, EPDM, SBR) are polymers with large elastic deformation (gaskets, bearings, sealants).
Common plastics in buildings
| Plastic | Building uses |
|---|---|
| uPVC / PVC | Water supply and drainage pipes, window and door frames (uPVC), electrical conduits, flooring, roofing sheets, cable insulation, waterproofing membranes |
| CPVC (chlorinated PVC) | Hot and cold water pipes |
| HDPE | Water tanks, pipes (water supply, gas), geomembranes, geogrids |
| LDPE | Films, damp-proof membranes, vapour barriers |
| Polypropylene | Pipes (PPR — hot water), fibres in concrete, geotextiles |
| Expanded and extruded polystyrene (EPS, XPS) | Thermal insulation boards, lightweight fill |
| Polyurethane (PUF) | Rigid insulation foam (sandwich panels), sealants, coatings |
| Acrylic (PMMA) | Transparent sheets, domes, signage, sanitaryware (acrylic bathtubs) |
| Polycarbonate | Impact-resistant transparent roofing and skylights, multiwall sheets |
| Melamine and phenolic resins | Decorative laminates (e.g. high-pressure laminates), adhesives, plywood glues |
| Epoxy and polyester resins | Adhesives, floor coatings, repair mortars, FRP composites |
| Silicone | Sealants, water repellents |
Moulding and forming processes
Compression moulding (thermosets), injection moulding (thermoplastic fittings), extrusion (pipes, profiles, sheets), blow moulding (tanks, bottles), rotational moulding (water tanks), calendering (films, sheets, flooring), thermoforming, casting and laminating.
Advantages and limitations of plastics
| Advantages | Limitations |
|---|---|
| Light weight | Low modulus of elasticity — flexible, large deflections |
| Corrosion and chemical resistance | Creep under sustained load, even at room temperature |
| Easy to mould into complex shapes; good finish and colour | High thermal expansion — needs expansion allowance |
| Good thermal and electrical insulation | Combustible; many emit smoke and toxic gases in fire |
| Low maintenance; waterproof | UV degradation (unless stabilised); brittle at low temperatures (some) |
| Economical in mass production | Environmental concerns — non-biodegradable waste |
Composite materials
A composite combines two or more distinct materials — a matrix and a reinforcement — to obtain properties better than either alone (e.g. RCC, ferrocement, FRP).
Fibre-reinforced polymers (FRP)
| FRP | Fibre | Features |
|---|---|---|
| GFRP | Glass fibres | Economical, corrosion resistant, lower modulus (larger deflections) — rebars, pipes, tanks, panels, gratings |
| CFRP | Carbon fibres | Very high strength and stiffness, light, excellent fatigue resistance, costly — strengthening and retrofitting (wraps, laminates), prestressing tendons |
| AFRP | Aramid fibres (e.g. Kevlar) | High toughness and impact resistance — protective applications |
| BFRP | Basalt fibres | Emerging economical alternative |
Matrices: polyester, vinyl ester, epoxy (best for structural bonding).
Manufacturing: hand lay-up, pultrusion (constant cross-section profiles and rebars), filament winding (pipes, tanks), resin transfer moulding.
FormulaRule of mixtures (longitudinal properties of unidirectional composites)
= modulus; = volume fraction; subscripts composite, fibre, matrix.
Applications in civil engineering:
- FRP rebars (GFRP/BFRP) in corrosive environments — marine structures, bridge decks, chemical plants.
- Strengthening and retrofitting — CFRP/GFRP sheets wrapped around columns (confinement), bonded to beams and slabs (flexure and shear) — seismic retrofit.
- Pultruded structural sections, footbridges, cooling towers, pipes, water tanks, cladding panels.
Properties: high strength-to-weight ratio, corrosion and chemical resistance, electromagnetic transparency, fatigue resistance (CFRP); but linear elastic, brittle failure (no yielding), vulnerable to fire and high temperatures (matrix softening), UV degradation (unprotected), high cost, bond and anchorage design needed.
Other composites in buildings
| Composite | Description / use |
|---|---|
| Sandwich panels | Two thin stiff facings (steel, aluminium, FRP) with a lightweight core (PUF, EPS, mineral wool, honeycomb) — insulated roofing, walls, cold storage |
| Aluminium composite panels (ACP) | Two aluminium skins with a core (polyethylene or fire-retardant mineral core) — facade cladding; fire-retardant cores are important for fire safety in tall buildings |
| Fibre cement boards and sheets | Cement with cellulose or synthetic fibres (asbestos-free) — roofing, cladding, partitions, ceilings |
| Glass fibre reinforced gypsum / concrete (GFRG, GFRC) | Gypsum or concrete panels with glass fibres — rapid walling systems, architectural elements |
| Wood–plastic composites (WPC) | Wood fibres/flour with thermoplastics — decking, door frames, panels (moisture and termite resistant) |
| Bamboo and natural fibre composites | Sustainable boards and panels |
| Reinforced concrete and ferrocement | Classic cement-based composites |